FLIGHT International, 23 May 1963 751
Double-slotted flaps on the wings and special control surfaces on
the nose give the Wren 460 a speed range extending to below
26 m.p.h. (see "Introducing the Wren")
S PORT
AND
B U S I N ESS
Introducing the Wren Flight tests have been completed on the
Wren 460, a modification of the Cessna 180 designed by Wren Air
craft Corporation of Fort Worth to combine normal light-aircraft
cruise performance with exceptional low-speed manoeuvrability.
The aircraft has been developed as a commercial application of the
ULS (ultra low speed) control system recently tested by the US
Army on James Robertson's experimental Skyshark aircraft, and is
described by the company as the first HTOL (heliport take-off and
landing) aeroplane. At gross weight under zero-wind, standard-
atmosphere, sea-level conditions the aircraft is stated to take off
in under 300ft and land in less than 200ft—well within the
400ft dimension suggested by the Federal Aviation Agency for
heliports.
The level-flight speed range quoted for the Wren 460 is from
under 26 m.p.h. to over 160 m.p.h. The slow-speed performance
stems from full-span, double-slotted flaps which can be lowered to
one of four positions (15°, 35°, 45°, and 60"). At the fully extended
60° position the lift of the wing is almost tripled and the drag is
quadrupled.
The ULS control surfaces, mounted on the nose of the aircraft
directly behind the propeller, serve to deflect the slipstream and to
produce powerful control forces at low airspeeds. The effective
ness of the normal elevators decreases sharply as the speed of the
aircraft is reduced, while that of the ULS surfaces increases (as
power is increased to offset the drag produced by the extended
flaps). On the Army's Skyshark aircraft, ULS nose controls are
used to provide control in pitch, yaw and roll. On the Wren 460,
which does not fly as slowly as the Skyshark, the normal rudder
and ailerons are sufficiently effective so that pitch control is the
only ULS control needed.
The ULS controls are integral with the elevator controls by a
direct push-rod linkage to the control yoke, and they operate in
conjunction with the normal elevators at all times. Compared with
the elevators the ULS controls are of small area, and so have only
limited effect during cruising conditions, when the slipstream is
only slightly faster than the airflow over the entire aircraft includ
ing the elevators. As the speed of the aircraft decreases and power
is applied to maintain slow flight, the ULS controls take a bigger
"bite."
The Wren 460 incorporates a number of other unusual design
features. A set of rotatable "teeth" or spoilers are located ahead
of the ailerons on the upper surface of each wing. These are con
nected directly to the aileron control linkage, and serve to eliminate
the adverse yaw which accompanies large aileron deflections at low
speeds. Normally "feathered," the spoilers rotate to provide extra
drag when the aileron behind them is deflected upwards.
To delay the stall at slow speeds, the full length of the leading
edge of the wing has been "augmented" by a wrap-around cuff of
sheet metal which enlarges the radius of the leading edge and
causes a slight "drooping" appearance in cross-section. Stalls are
reported to be extremely gentle.
The height of the rudder and fin has been increased by eleven
inches. The only change in the cockpit is the addition of an LSI,
or low speed indicator, driven from an anemometer mounted on
the starboard wing strut. The company report that the only ad
verse effect of the addition of the new devices is a decrease of
approximately four per cent in the high-speed capabilities of the
aircraft. Production versions of the Wren will use new production
Cessna 180/182 airframes; the power unit is a Continental O-470-R
rated at 230 h.p. at 2,600 r.p.m., driving an 82in diameter constant-
speed propeller. At a gross weight of 2,8001b, the aircraft carries
four people and cruises at 153 m.p.h. at 75 per cent power at
6,500ft.
—and the Derringer Illustrated below, the Derringer twin-
engined two-seat business aircraft is currently being developed by
Wing Aircraft Company of Torrance, California. Powered by two
115 h.p. engines, the prototype Derringer made its first flight in
May 1962; production versions, powered by two 150 h.p. Ly-
comings, are now under construction at Torrance. Further pro
duction is expected to start in Okmulgee, Oklahoma, in 1964. The
unusual formula of a twin-engined machine carrying only two
people was selected after Wing had carried out surveys which indi
cated that more than 57 per cent of all flights in four- to seven-seat
aircraft were made with only two people aboard; and that twin-
engined types were 1.5 times as active "in trip frequency" as single-
engined craft.
The Wing Derringer, described
above, has a cruising speed of
225 m.p.h. Gross weight is
2,6801b, span is 29ft 2in, and
basic price is $27,500
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